Many of today’s high-performance technologies — nuclear reactors, spacecraft, concentrated solar plants, and hydrogen cells — require advanced materials. Advanced means they are made of metals and ceramics that can withstand extreme conditions or meet exacting specifications.
In the past, these advanced materials were typically manufactured from powder that was poured into a die, subjected to high pressure and slowly heated in a process called hot pressing. However, hot pressing results in waste heat, contributing to high costs. Those costs have limited the widespread use of advanced materials in industries that manufacture everyday items such as automobiles.
More recently, engineers have developed a cost-saving process called spark plasma sintering (SPS). Instead of heat, SPS sends electricity through the die, and sometimes the material itself, to fuse the molecules of powdered metals, ceramics, or a mixture of both.
Now, Idaho National Laboratory has developed world-class capabilities to help industry design efficient SPS manufacturing processes. The lab’s newest addition, one of the largest machines of its kind in the world, makes it possible to manufacture new materials at industrially relevant scales.
“The SPS process is much faster, much more energy efficient, and more capable of maintaining the original, superior powder properties in the fully sintered part,” said Troy Holland, a Senior SPS Materials Scientist/Engineer at INL.
Maintaining the properties of the original powdered material is important because of the often-stringent performance requirements of these parts. “If you heat them up for a long time you often lose the benefits that you had in the original powder,” Holland said.
INL has designed and built four custom SPS machines that range from supporting small experiments on the bench-scale to industrial-scale, large-format, high-throughput systems.
As its name implies, the Nano-SPS is a small machine that can fuse together metal or ceramic powder to make parts from the nano- to micrometer scales. The Nano-SPS isn’t made for building commercial parts, per se, but is an experimental machine that can help researchers predict and control the nanostructure and microstructure of a component by observing how powder materials flow and interact at nanometer resolution.
X-ray and neutron diffraction experiments using the Nano-SPS setup provide real time data about chemical and microstructure evolution during the SPS process.
Understanding how the powder molecules interact during SPS, from atomic bonds to local nanostructures to microstructures, is important because variation at these scales can make a big difference in performance.
“Our goal is to understand and control the process well enough to be able to control local microstructures of parts,” Holland said, “This allows us to minimize variation or take advantage of local intentional variation within the part in as repeatable a way as possible to produce prequalified parts.”
The next machine, the Micro-SPS, can manufacture parts from roughly micrometer to centimeter scales and is also useful in understanding microstructural evolution. The Micro-SPS is used to determine bulk material sintering kinetics data. It does this by providing windows into the tooling to support real time X-ray and neutron radiography of bulk SPS processing.
SPS is also an emerging technology for advanced nuclear fuels fabrication. The Radiological Spark Plasma Sintering System (RSPS) at INL’s Materials and Fuels Complex is a purposefully engineered system that is integrated within a radiological work glovebox.
The DCS-800 is a larger SPS machine that can make parts up to about one square meter in size. Located at INL’s Energy Systems Laboratory, the DCS-800 operates at high power, high temperatures and high pressure. It allows materials that have been discovered on the bench scale to be demonstrated at industrially relevant scales.
Finally, the Roller SPS will allow INL experts to spark plasma sinter continuous sheets of material from powders. That means they can make parts of unlimited size, while further decreasing the energy use and manufacturing time.